This invention relates to bogies for railed vehicles.
Known bogies for railed vehicles, such as commuter or shorthaul rail vehicles or tram cars, have primary springs which operate against bogie frames to allow for relative upward and downward movement of the bogie frames and the bogie wheels. Secondary springs are provided between a bogie frame and a car or vehicle body to provide a secondary spring action. In such bogies, it is also conventional to provide wheels in sets with the sets spaced longitudinally of the bogie and the wheels of each set spaced laterally of the bogie. One set of wheels are normally provided as idle or nondriven wheels which are rigidly connected to a wheel mounting frame, for example by pedestal bearings, with the wheel mounting frame extending transversely of the bogie frame and coupling by bearing arrangements to a transversely extending frame member of the bogie frame. The bogie and wheel mounting frames are relatively immovable longitudinally of the bogie except for vertical pivoting movements of the mounting frame upon the bogie frame allowed for by the bearing arrangements. The latter also permit lateral movement of the mounting frame between limits, such lateral movement, for instance, being caused by an axial load placed against a flange of a wheel by a rail when the bogie is travelling along rails.
Such a bogie is described in U.S. Pat. No. 4,941,409 issued Jul. 17, 1990, to which the reader is directed for reference, which is incorporated herein by reference, and in its German equivalent, Offenlegungschrift number 3,808,593. The bogie structure described therein is suitable for use when a vehicle or car is for travelling around rail curvatures of large radius, but when travelling around small radius curvatures, the movement available to the wheel mounting frame may not enable its wheels to accommodate the curvature of the rails without undue resistance. As a result, undue pressure is applied either to one wheel flange or the other during travel around curvatures of small radius. This pressure, assisted by the slippage between the rail and the radial surface of the wheel flange, results in inordinate wear of the engaging surfaces. This undesirable result is found even though negligible wear between rails and wheel flanges results when the bogie travels in a straight line.
The present invention seeks to provide a bogie which is capable of being used on rails having path curvatures of any acceptable radius while mitigating the above problem.
Accordingly, the present invention provides a bogie comprising:
a bogie frame extending in a longitudinal direction of the bogie;
at least two bogie wheel sets spaced longitudinally of the bogie with the wheels of each set spaced apart laterally of the bogie;
a wheel mounting frame extending transversely of the bogie frame and rotatably carrying the wheels of one of the wheel sets; and
a coupling arrangement coupling the wheel mounting frame to the bogie frame, the coupling arrangement permitting pivoting of the wheel mounting frame about a vertical pivot axis and permitting limited lateral movement of the wheel mounting frame relative to the bogie frame, the coupling arrangement being configured to translate lateral forces exerted upon one or other of the wheels carried by the wheel mounting frame to provide a component of force acting to rotate the wheel mounting frame relative to the bogie frame and turn the wheel set mounted thereupon so as to reduce said lateral force.
The wheel mounting frame may be coupled to the bogie frame by way of an intermediate member suspended from a cross member of the bogie frame. The coupling arrangement may then comprise pivot means coupling the intermediate member to the bogie frame and coupling mechanisms coupling the intermediate member to the wheel mounting frame.
In a particularly practical and desirable arrangement, both the intermediate member and the wheel mounting frame are disposed at positions lower than the height of the bogie frame at positions between the sets of wheels. This desirable arrangement allows the car or vehicle body to be disposed at a particularly low level, with floor height of as little as 30 cms. being possible.
The pivot means may comprise two resilient connection arrangements which are spaced-apart longitudinally of the bogie to provide a pivot axis, for the wheel mounting frame, at a position between the connection arrangements. With the connection arrangements disposed in tandem along the longitudinal axis of the bogie frame, a pivoting movement of the wheel mounting frame and accompanying set of wheels is possible up to an angle of approximately 1.5 to 3. The resilient connection arrangements preferably each comprise a rigid spindle with an upwardly extending (e.g. substantially vertical) major axis, a resiliently deformable surround, for example of elastomeric material, bonded to the spindle, and an outer rigid sleeve member bonded to the surround. Such a structure advantageously allows the rigid sleeve member and the spindle to tilt relative to each other in any direction, i.e. universally.
The coupling mechanisms may each comprise a cylindrical metal arbour, surrounded by an elastomeric layer which is encased by a metal sleeve which is a press fit in a housing element, specifically a journal boss, of the intermediate member. The metal arbour may then have reduced diameter bearing journals positively located in supports mounted to the intermediate member.
The two coupling mechanisms connecting the wheel mounting frame to the intermediate member may be disposed one on each side of a longitudinal axis of the bogie. Interengaging parts of each coupling mechanism may slide relative to each other along an axis which is inclined at an angle, preferably 10 to 40, to the longitudinal axis of the bogie. With this latter arrangement, and with the directions of action being at opposite angles to the longitudinal axis, any lateral movement of the wheel mounting frame is accompanied by a slight pivoting movement of the wheel mounting frame. The force applied to the one wheel by a curved rail will be transmitted to the inclined coupling mechanisms and result in a component of force acting to pivot the wheel mounting frame so as to tend to reduce the load upon the wheel flanges, thereby reducing wear. The pivoting movement of the wheel mounting frame upon the two coupling mechanisms is accommodated by the coupling mechanisms until the limit of the elastic play between the metal sleeves and supports is reached, whereupon the lateral load is transmitted through the intermediate frame to the central pivot between the intermediate frame and the bogie frame member.
A compound movement of the wheel mounting frame is thus made possible, with the pivoting movement of the wheel mounting frame taking place about a pivotal point in the middle between the centring bearings. The elastic coupling between the wheel mounting frame and the intermediate beam on the one hand and the intermediate beam and the bogie transverse beam on the other hand cause a superimposed movement in opposite directions, through which automatic radial adjustment of the wheel pairs is achieved.
It has been found that a suitable compound movement can be achieved with the relationships between the various factors adjusted as follows:
the resiliently deformable sleeve has a Shore hardness of from 50 to 80;
the resiliently deformable surround has a Shore hardness of from 40 to 70;
the angle of inclination between the longitudinal axis of the bogie and the direction of action of each coupling mechanism is from 10 to 40 with the directions of action oppositely inclined;
the distance between the coupling mechanisms is between 300 and 800 mm; and
the distance between axes of the resilient connection arrangements of the central pivot is between 100 and 250 mm.
The above and other objects and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same element.